1. Field of the Invention
The present invention relates to a method and apparatus for pass/fail determination of bonding for use in bonding apparatuses and to a structure of a bonding apparatus for pass/fail determination of bonding.
2. Description of the Related Art
In semiconductor manufacturing processes, wire-bonding apparatuses are often used for bonding of thin metallic wires to electrode pads on a semiconductor chip and electrode leads on a lead frame for connection therebetween. Many wire-bonding apparatuses include a bonding arm configured to be rotated with a drive motor, an ultrasonic horn attached to the bonding arm, a capillary attached at one end of the ultrasonic horn, and an ultrasonic vibrator attached to the ultrasonic horn. In such wire-bonding apparatuses, the bonding arm is driven and rotated to move the capillary in a direction toward and away from a pad or lead and to press and bond an initial ball formed at a tip end of the capillary or a wire to the pad or lead, and then the ultrasonic horn is resonated by the ultrasonic vibrator to provide ultrasonic vibration at the tip end of the capillary for bonding operation.
In the case of bonding using such a wire-bonding apparatus, an initial ball formed at a tip end of a wire that is inserted through the capillary collides with a pad at a certain speed and then is pressed and bonded at a constant load to the pad to be a bonded ball. The collision causes the wire and capillary to vibrate in the pressing direction also during the subsequent period of pressing at the constant load, and thereby the pressing load to fluctuate and the shape and diameter of the bonded ball to vary, which can result in defective bonding. Also in the case of an initial ball formed defectively smaller than a predetermined size, the pressing load can fluctuate to result in defective bonding.
To address the problem, wire-bonding apparatuses generally include an encoder provided in a bonding head to detect the change in the height position of the capillary, in which a detection output of the encoder is fed back to a controller to control the output of the drive motor and thereby to prevent the pressing load from fluctuating. However, since the encoder cannot detect the pressing load on the wire directly, the fluctuation of the pressing load cannot be suppressed sufficiently only by feed-backing the output of the encoder.
Hence, there has been proposed a method in which a pressure sensor is provided between an ultrasonic horn and a bonding arm to detect pressing load, and the drive motor is controlled by the pressing load to suppress the vibration of the capillary and thereby to make the pressing load constant (see Japanese Unexamined Patent Application Publication No. 2003-258021, for example).
In addition, if there is mechanical loosening or wear on the bonding arm and/or capillary, a force of impact when a wire on the capillary collides with a pad on a semiconductor chip during wire-bonding operation can cause chip damage in which such as the semiconductor chip has cracks thereon. To address this problem, there has been proposed a method in which an impact sensor for measuring a force of impact is attached to the bonding stage and, based on the difference between a detected waveform and a reference waveform, an alarm is generated to notify of the existence of mechanical loosening or wear on the bonding arm and/or capillary (see Japanese Unexamined Patent Application Publication No. 7-74215, for example).
In contrast, in the case of bonding between a semiconductor chip and a substrate, multiple pads on the semiconductor chip are connected sequentially to multiple leads on the substrate. During such bonding operation, even if there can be no loosening or wear on the bonding arm and/or capillary and the pressing load from the capillary onto the pads can be controlled at a predetermined value, there may occur defective bonding such as abnormal ball deformation and/or chip damage. However, the related arts described in Japanese Unexamined Patent Application Publication Nos. 2003-258021 and 7-74215 cannot detect defective bonding, if any, during the bonding operation before a visual inspection step for bonded portions to be performed after the bonding between multiple pads on the semiconductor chip and multiple leads on the substrate has been completed. This suffers from a problem of taking a long time for product revision. Further, if the manufacturing process includes no visual inspection step for bonded portions, defective products, if any, cannot be found before the final inspection step, suffering from a problem of reduction in production yield.